The Specialty Coffee Association publishes a water quality standard for brewing, and it is the reference most recipes are built against.
The targets
Odour — clean, free of any smell. Colour — clear. Chlorine — zero. TDS — around 150 mg/L, acceptable 75 to 250. Calcium hardness — around 68 mg/L as CaCO₃, acceptable 17 to 85. Total alkalinity — around 40 mg/L, acceptable at or near that. pH — around 7, acceptable 6 to 8. Sodium — around 10 mg/L.
What each does
Hardness — calcium and magnesium extract flavour compounds. Too little gives hollow, empty coffee; too much gives chalky harshness and scale.
Alkalinity — buffers acidity. Too high and the coffee tastes flat and dull, with the acidity neutralised. This is the most commonly wrong parameter in tap water.
Chlorine — tastes and smells of chlorine, unmistakably, and it must be zero.
The criticism
The standard is a compromise range, and many roasters and competitors deliberately brew outside it — higher magnesium, lower alkalinity — for more expressive results.
It is a good default, not a ceiling.
Testing yours
Aquarium or pool test strips measure hardness and alkalinity adequately for this purpose and cost very little.
Your water utility also publishes annual quality reports with the numbers.
Last reviewed 8 August 2026